In recent years, the HSDPA method, which greatly improves radio communication transmission speed, has been studied by the 3GPP (3rd Generation Partnership Project) As HSDPA channels in the HSDPA method, an HS-PDSCH (High Speed Physical Downlink Shared Channel) for packet data and an HS-SCCH (High Speed Shared Control Channel), which is a control channel that transmits a channelization code, multiplexing and modulation method information, and so forth, necessary for receiving this HS-PDSCH, are stipulated as a downlink (hereinafter referred to as “DL”) that transmits radio signals from a base station apparatus to a mobile station, and these channels are transmitted as a set.
With the HSDPA method, an HS-DPCCH (High-Speed Dedicated Physical Control Channel) is stipulated as an uplink (hereinafter referred to as “UL”) that transmits radio signals from a mobile station to a base station, and ACK/NACK signals indicating whether or not an HS-PDSCH radio signal has been received normally by a mobile station, and information on downlink propagation path quality between a mobile station and base station—specifically, a CQI (Channel Quality Indicator)—are transmitted by this HS-PDSCH. This CQI is generated based on an SNR (Signal to Noise Ratio) calculated from a CPICH (Common Pilot Channel), which is one of the DL channels, and the reference period for measurement of this SNR is called a Measurement Reference Period. The SNR is a measure indicating the propagation path conditions, and when a base station receives a CQI generated based on a high SNR, it can increase the HS-PDSCH transmission rate.
FIG. 1 shows the frame formats of an HS-SCCH, HS-PDSCH, and HS-DPCCH. With an HS-SCCH, HS-PDSCH, and HS-DPCCH, a subframe unit is composed of 3 slots. One subframe of these channels is 2 ms, and therefore five subframes of these channels are contained in one receive frame (10 ms) of a normal channel such as a DL-DPCH (Down Link Dedicated Physical CHannel) or CPCIH.
FIG. 2 shows the CPICH frame format and a more detailed illustration of the HS-DPCCH frame format. A CPICH is composed of 15 slots, this unit being called a frame. One CPICH frame is 10 ms. On the other hand, in the case of an HS-DPCCH, the first slot of any subframe is an ACK/NACK field containing an ACK/NACK signal, and the next two slots comprise a CQI field holding a CQI. An HS-DPCCH corresponding to one CPICH frame is composed of five packet data units—that is, subframes. The five HS-DPCCH subframes are designated Subframe #0, Subframe #1, Subframe #2, Subframe #3, and Subframe #4.
FIG. 3 shows the timing relationship between a CPICH measurement reference period—the basic unit used in SNR measurement—and HS-SCCH, HS-PDSCH, and HS-DPCCH subframes. Transmission from a base station is always performed with HS-SCCH slot boundaries and CPICH slot boundaries aligned, and an HS-SCCH and HS-PDSCH are transmitted as a subframe unit set with a 2-slot offset. An ACK/NACK signal corresponding to an HS-PDSCH subframe is stored in the HS-DPCCH ACK/NACK field following the elapse of 7.5 slots after reception of that subframe is started by a mobile station, and is transmitted from the mobile station to the base station.
On the other hand, a CQI transmitted held in the CQI field of an HS-DPCCH subframe is generated based on the SNR value calculated from the CPICH included in the DL every period specified by a higher-level layer—that is, every measurement reference period—irrespective of HS-PDSCH reception by a mobile station. In FIG. 3, the CQI transmitted in CQI field (n), for example, is generated based on the SNR calculated from the 3-slot measurement reference period CPICH that ends one slot before the start of CQI field (n).
The cycle for actual CQI transmission by a mobile station to a base station in the HS-DPCCH CQI field is specified by a higher-level layer. The cycle at which this CQI is actually transmitted is called the Feedback Cycle, k.
FIG. 4 shows the timing relationship between the HS-DPCCH subframe configuration and the measurement reference period corresponding to the CQI field of that subframe when feedback cycle k=1. As can be seen from FIG. 4, when feedback cycle k=1, a CQI is stored in the CQI field of all HS-DPCCH subframes. FIG. 5 shows the timing relationship between the HS-DPCCH subframe configuration and the measurement reference period corresponding to the CQI field of that subframe when feedback cycle k=3. As can be seen from FIG. 5, when feedback cycle k=3, a CQI is transmitted from the mobile station to the base station at a frequency of once every 3 times with regard to HS-DPCCH subframe units. An HS-DPCCH period in which a CQI stipulated by feedback cycle k is actually transmitted is called a “scheduled period” (also referred to in the drawings as “Scheduled pattern of CQI reports”), and CQI fields in all HS-DPCCH subframes are called “postulated periods” without regard to stipulation by feedback cycle k. Therefore, when feedback cycle k=1, all postulated periods are scheduled periods, but when feedback cycle k=3, one of three postulated periods is a scheduled period.
Next, compressed mode will be described, taking the HSDPA method as a concrete example. In cellular radio communications, different frequency bands may be used by cells of different communication methods, such as a W-CDMA cell and a GSM cell, or by cells of the same method, and in order for a mobile station to perform handover between such cells of differing frequency bands, the mobile station must receive a signal of another frequency band transmitted from the base station of another cell while communicating with the base station of the cell to which it currently belongs, and acquire beforehand information relating to the base station of the other cell. Thus, with the HSDPA method, it is stipulated that an interval (DL transmission gap interval) is to be provided in which a DL is not used to the extent that a mobile station and a base station communicating with the mobile station do not adversely affect communication, and that the mobile station should acquire control information relating to the base station of another cell in this DL transmission gap interval. The method whereby an interval is provided in which communication between a base station and mobile station is halted in HSDPA radio communication is known as compressed mode. In compressed mode, a transmission gap interval may be provided only in a UL, or may be provided in both the UL and DL. Furthermore, in compressed modes in methods other than HSDPA, also, downlink propagation path quality information is transmitted from a mobile station to a base station by means of virtually the same method as described above.
FIG. 6 shows an example of the timing relationship between a DL transmission gap interval, measurement reference periods, and a UL transmission gap interval in the case where feedback cycle k=1 in the compressed mode being standardized by the 3GPP. The timing relationship between the DL transmission gap interval and UL transmission gap interval is not necessarily as shown in FIG. 6, but depends on the compressed mode stipulations.
If a measurement reference period and DL transmission gap interval overlap, an SNR cannot be calculated accurately for that measurement reference period even if the overlap includes only part of the measurement reference period. Therefore, CPICH measurement reference period Reference Periods_C shown in FIG. 6 is not used, but instead a CQI is generated based on immediately preceding measurement reference period Reference Periods_B that does not overlap the DL transmission gap interval, and this generated CQI is transmitted from the mobile station to the base station in the first HS-DPCCH scheduled period CQI_C after the end of the UL transmission gap interval. DTX (Discontinuous Transmission) is stored in the CQI field instead of a CQI in scheduled periods in the UL transmission gap interval.
Next, an example of the timing relationship between a DL transmission gap interval, measurement reference periods, and a UL transmission gap interval in the case where feedback cycle k=4 in compressed mode is shown in FIG. 7. In FIG. 7, since feedback cycle k=4, the frequency of appearance of a scheduled period with respect to a measurement reference period is ¼. Therefore, in FIG. 7, instead of using measurement reference period Reference Periods_E partially overlapping the DL transmission gap interval, a CQI is generated based on the received signal of immediately preceding measurement reference period Reference Periods_B that does not overlap the DL transmission gap interval, and this generated CQI is transmitted from the mobile station to the base station in the first HS-DPCCH scheduled period CQI_E after the end of the UL transmission gap interval. With regard to these points the situation in FIG. 7 is similar to that in FIG. 6, but in FIG. 7, as feedback cycle k=4, a CQI is generated based on the measurement reference period Reference Periods_B received signal which should not really be used for CQI generation, and moreover a CQI is specially generated based on the measurement reference period Reference Periods_F immediately after measurement reference period Reference Periods_E, and this CQI is transmitted from the mobile station to the base station in postulated period CQI_H, which is not a scheduled period. A CQI transmitted from the mobile station to the base station in postulated period CQI_F which is not a scheduled period in this way is called an extra CQI.
Timing relationships between a DL transmission gap interval, measurement reference periods, and a UL transmission gap interval as shown in FIG. 6 and FIG. 7 are described in Non-patent Document 1.
Non-patent Document 1: Title: “CQI reporting in DL Compressed Mode”, Source: Philips, 3GPP TSG RAN WG1#33, Agenda Item: 5.3, Document No: Tdoc R1-030742, New York, USA, 25th-29th Aug. 2003